Automated systems exist for collecting data from meters that measure usage of resources, such as gas, water and electricity. Such systems may employ a number of different infrastructures for collecting this meter data from the meters. For example, some automated systems obtain data from the meters using a fixed wireless network that includes, for example, a central node in communication with a number of endpoint nodes (e.g., meter reading devices (MRDs) connected to meters). At the endpoint nodes, the wireless communications circuitry may be incorporated into the meters themselves, such that each endpoint node in the wireless network comprises a meter connected to an MRD that has wireless communication circuitry that enables the MRD to transmit the meter data of the meter to which it is connected. The endpoint nodes may either transmit their meter data directly to the central node, or indirectly though one or more intermediate bi-directional nodes which serve as repeaters for the meter data of the transmitting node. Some networks operating in this manner are referred to as “mesh” networks.
Although the fixed wireless network infrastructure is an efficient infrastructure for collecting data from MRDs, there are a number of scenarios in which a fixed wireless network may, at least temporarily, not be an optimal infrastructure for collecting data from at least some of the MRDs in a particular metering system. In particular, for an operator of a metering system, setting up, expanding, and/or maintaining a large fixed wireless network may require a significant investment of financial capital. Additionally, setting up or expanding a large fixed wireless network may require time to plan the location of each node in the network, time to build up and/or access each location, and time to actually install the necessary wireless communications equipment at each location. Thus, for example, in some scenarios, a metering system operator may simply not yet have enough financial capital or the necessary time to build a new wireless network or expand an existing wireless network to include certain MRDs within the system. This is especially true for outlying MRDs that are located along the geographic boundaries of the system or in sparsely populated or sparsely developed areas. These MRDs may be located too far away to transmit their metering data to any of the existing repeater nodes in an existing fixed wireless network. Thus, it may be advantageous to defer building or expanding a wireless network to include these outlying MRDs until the outlying locations become more populated or developed or until the costs associated with building or expanding the wireless network can be otherwise incurred.
In these and other scenarios, until the fixed wireless network is built or expanded to include these MRDs, other network infrastructures may be at least temporarily employed to collect the meter data from the MRDs. One such other network infrastructure, which will hereinafter be referred to as the “mobile data collection” infrastructure, involves the use of a mobile data collection device, or interrogator, that can be transported to the site of each MRD to collect the meter data from each MRD. The mobile infrastructure may employ data collection techniques that are commonly referred to as “walk by” or “drive by.” The “walk by” techniques may involve the use of a smaller size mobile data collection device which can be transported by one or more people on foot. The “drive by” techniques may involve the use of a somewhat larger mobile data collection device that is transported by a vehicle such as a van or small truck. The “walk by” techniques are thus more suitable for MRDs that are dispersed throughout smaller areas or areas that cannot be accessed using a vehicle. The “drive by” techniques are thus more suitable for MRDs that are dispersed throughout larger areas that are vehicle accessible.
In order to enable MRDs in mobile data collection networks to send out a higher powered transmission signal while still conserving the long term power supply of the meters, some conventional mobile data collection networks have employed a sleep/wake cycle to regulate transmission of meter data from the MRDs. The idea behind the sleep/wake cycle is that it is only necessary for an MRD to transmit its meter data while the mobile data collection device is within the transmission range of the MRD. Thus, the mobile data collection device will transmit a “wake signal” to notify a particular MRD that the mobile data collection device is approaching the physical proximity of the MRD. Accordingly, the MRD will typically begin its operation in the low power sleep mode in which it does not transmit meter data. Then, when the mobile data collection device approaches the MRD, the MRD will receive the wake signal from the mobile device. The wake signal will cause the MRD to “wake up” and transition into a higher power wake mode in which it transmits its meter data to the mobile device. Then, after transmitting its meter data, the MRD will transition back into the sleep mode, thereby once again conserving its power supply.
In some conventional mobile data collection networks that employ sleep/wake cycles as described above, the mobile data collection device transmits the wake signal to the MRD using an unlicensed frequency band, such as an Industrial, Scientific, and Medical (ISM) band. Examples of ISM bands include frequency bands having respective center frequencies of 915 MHz and 2.4 GHz. Using unlicensed frequency bands affords certain advantages for battery-powered MRDs. For instance, unlicensed frequency bands generally support wide bandwidths and, therefore, high bitrates for communication of large blocks of data, as may be collected in MRDs. Further, the regulatory rules for unlicensed frequency bands are written to allow a large number of devices to coexist. This feature may be particularly advantageous in the context of networks in which many MRDs are deployed, such as, for example, networks operated by large electric, gas, or water utilities.
Although using an unlicensed frequency band to wake MRDs through carrier-sensed radio receivers results in some advantages, this technique also suffers from certain drawbacks. For example, unlicensed frequency bands are often crowded with large numbers of communication devices of many different manufacturers and types. As a result, particularly in densely populated areas, any particular channel of the unlicensed frequency band may have large amounts of traffic. This traffic can cause interference that results in false wakeups. That is, MRDs may transition to the higher power wake mode even when no mobile data collection device, or interrogator, is within range. These false wakeups may increase power consumption and adversely affect the battery life of the MRDs.
Even so-called spread spectrum devices can be affected by false wakeups. Further, spread spectrum techniques, such as direct sequence spreading or frequency hopping, add another challenge for operating battery-powered MRDs in unlicensed frequency bands. Spread spectrum techniques typically require lengthy and complex methods for the receiver in the MRD to become frequency-, time-, and/or code-synchronized with the transmitter in the interrogator. These methods put an undesirable drain on battery-powered MRDs, especially if the process has to be repeated due to false wakeups.
Thus, there is a need in the art for a meter data collection system in which false wakeups and interrogator-MRD synchronization time are reduced while maintaining communication throughput.